1. Field of the Invention
The present invention is directed to a thin film calorimeter for measuring an exothermic reaction when ultraviolet (UV) light is directed onto a precise thickness and area of a specimen or on a precise weight of a solution, which has monomers and UV photo initiators therein to determine a “factor of curability”.The “factor of curability” can be: the peak BTU's per/hour during the curing, the total BTU's generated from the curing, the time to reach the peak BTU per hour or the log of the time to peak temperature divided by the log of the slope of the curve of the time to reach the peak temperature. The UV curable solution can be an ink, a coating or an adhesive.
2. Description of the Related Art
In the curing of inks, coatings and adhesives having photo initiators therein, the monomers and photo initiators are exposed to UV light such as from a mercury vapor light or from UV light emitting diodes (UV LEDs). When this takes place, the monomers and photo initiators are exothermically reacted, cured and polymerized into cross-linked polymers. This exothermic reaction, curing and polymerization often generates significant heat. The light intensity, wavelength of light and duration of the light to achieve complete curing has been studied over the years. Lately, interest in the curability of the ink, coating or adhesive has resulted in the development of techniques for determining or gauging curability to determine the quality and effectiveness of the cure.
One instrument (device) used was a differential scanning calorimeter.
However this instrument is expensive, often costing $75,000.00 or more. More recently the use of a thin film calorimeter has been proposed by T. M. Roper et al. in their paper entitled “Rapid Measurement of Photo-polymerization Kinetic Behavior Using a Thin-Film Calorimeter” published by the RadTech International trade show in Charlotte N.C., May 2-5, 2004. Their initial techniques have been improved upon by Control-Cure Inc. of Chicago, Ill.
Several “factors of UV curability” can be explored. One is the total heat generated. Another is the log of the time to peak temperature divided by the log of the slope of the curve of the time to the peak temperature. Still another is time to peak temperature.